The present invention relates to an engine ignition system adopted for power boost and fuel economy, which mainly comprises a diaphragm, a spring, a cylindrical housing with a variable resistor disposed therein and under the diaphragm and connected to an opening of the venturi tube of the throttle valve so to constitute the vacuum suction means which functions in instant response to the variation of the current of air/fuel mixture in the carburetor by producing suction force of different level on the diaphragm which can make the variable resistor change, effecting the timing actuation of transistors in the present circuit so to determine the charge and discharge time of a capacitor via an ignition signal, thus effecting the period of discharge of the ignition coil so to automatically adjust the extent of the ignition spark and to advance the ignition.
As it is well known that the engine ignition system is employed to provide a high-voltage current for the ignition plug so that spark can be generated across the gap of the plug to ignite the compressed mixture of the air and fuel each time when the piston reaches the top dead center (TDC) in a compression stroke; and the higher the engine speed reaches, the more the ignition is advanced so to give the air/fuel mixture ample time to burn and transmit maximum power to the piston. To effect this kind of ignition advance, generally there are adopted two types of spark-advance mechanisms, centrifugal and vacuum.
In the centrifual mechanism, as shown in FIG. 1, there are disposed two weights that throw out against spring tension as engine speed increases. This movement is transmitted through a toggle arrangement to the breaker cam. This causes the cam to advance, or move ahead, with respect to the distributor drive shaft.
In the vacuum mechanism, as shown in FIG. 2, it contains a spring-loaded and airtight diaphragm connected by a linkage to the breaker plate which is supported on a bearing so that it can turn with respect to the distributor housing. It actually turns only a few degrees, since the linkage to the spring-loaded diaphragm prevents any greater rotation than this.
The spring-loaded side of the diaphragm is connected through a vacuum line to an opening which is on the atmospheric side of the throttle valve when the throttle is in the idling position. There is no vacuum advance in this position.
As soon as the throttle is opened, however, it swings past the opening of the vacuum passage. The intake-manifold vacuum can then draw air from the vacuum line and the airtight chamber in the vacuum advance mechanism. This causes the diaphragm to move against the spring. The linkage to the breaker plate then rotates the breaker plate. This movement carries the contact points around so that the cam, as it rotates, closes and opens the points earlier in the cycle. The spark consequently appears at the spark-plug gap earlier in the compression stroke. As the throttle is opened wider, there will be less vacuum in the intake manifold and less vacuum advance. At wide-open throttle, there will be no vacuum advance at all. The spark advance under this condition will be provided entirely by the centrifugal advance mechanism.
On the magnetic-pick-up distributor, the vacuum advance mechanism is attached to the magnetic pick-up assembly so that this assembly is rotated to provide the vacuum advance.
From the above description of advance mechanisms, it is obvious to see that in correspondance to different engine speed, there is a various advance angle defined. In a typical example, the ignition takes place 8 degrees in advance to the reaching of the piston to the TDC; and at the speed of 1000 rpm, the centrifugal advance does not happen. At the speed of 2000 rpm, the corresponding advance angle is set at 26 degrees.
Generally speaking, the spark at the ignition plug must be generated before the piston reaches the TDC in the compression stroke. The start of the combustion as well as the producing of the pressure is allowable at the end of the compression stroke, during the period of the passing of the piston through TDC and the initial of the power stroke. If a delayed ignition takes place, with the piston having started to move downward, the pressure, produced by the combustion of the mixed air and fuel, can generate less power than it should do. In case the ignition occurs with too much advance, pressure from the combustion of the mixed air and fuel is built up to the peak before the end of the compression stroke, which will cause serious knocking and damage to the engine.
Thus, the operation power and life of the engine is closely associated with the precision of the ignition process, because sudden knocking can create huge impact on the crank shaft, causing serious damage of the bearings or even breaking cylinder parts into pieces.
Recently, more and more newly-built cars have adopted electronically controlled spark advance devices to replace those centrifugal and vacuum advance mechanisms for providing more precise and secure ignition, as shown in FIG. 3, a commonly used electronics type spark advance is illustrated.
However, this kind of electronic advance device is relatively expensive and is difficult to be compatible with the traditional centrifugal and vacuum advance mechanisms in installation when replacing the same by said electronic advance device.
In addition to the advance mechanism, the ignition system is also vital to the efficiency of combustion and ignition.
In a conventional engine ignition process, as one cylinder begins its compression stroke, one edge of the rotary cam in the distributor is moving away from the arm of a contact-point breaker, and a current is produced in the first coil when the contact points are in contact with each other so as to create a magnetic field thereon. Afterwards, the piston compresses the mixed air and fuel to a position of ignition. In the meantime the next breaker point of the cam begins to engage with the arm of the breaker so as to make the contacting points separate, terminating the flow of the current in the main circuit and causing the absence of the existing magnetic field. Thus a high voltage is produced on the second coil, and a spark is created between the spark gap of a plug as a result of the second coil being connected to said plug via the distributor cap as well as the rotor.
In design, the voltage output from the ignition cord can be varied from one to the other in accordance with the practical working condition; in principle, the basic requirement that a spark be produced across the spark gap must be met. For different spark gaps, different voltages are correspondingly defined accordingly. Moreover, the density and volume of the mixed air and fuel fed into the cylinders are varied in accordance with the extent of the opening of the throttle valve as well as the engine speed. To change the voltage of the spark, the high voltage produced in the ignition coil must be simultaneously varied for different working conditions.
The density of the air/fuel mixture in the compression stroke is variable by means of the carburetor, as a result of the ratio of the air and fuel being changed according to various working requirements; for example:
A. Idle speed circuit: denser air/fuel mixture is required to start a "cold" engine, as shown in FIG. 4, the closing of the throttle valve 3A produces a high proportion of fuel in the mixture. It leans out somewhat as it mixes with the small amount of air that gets past the closed throttle valve. The final mixture is still satisfactorily rich for the idle and low speed operation. PA1 B. Low speed circuit: As shown in FIG. 5, when the throttle valve 3A is opened slightly, fuel is thus fed into the intake manifold through the low-speed port. This fuel mixes with the additional air moving past the slightly opened throttle valve to provide sufficient mixture richness for part-throttle low-speed operation. PA1 C. High-speed part-load circuit: When the throttle volve is opened sufficiently, and the wider the throttle is opened and the faster the air flows through the air horn, the greater the vacuum in the venturi. This means that additional fuel will be discharged from the main nozzle (because of the greater vacuum). As a result, a nearly constant air-fuel ratio is maintained by the high-speed circuit from part-to wide-open throttle.
However, the high-voltage output of the ignition coil of the automobile ignition system is almost fixed without variation with respect to the change of the degree of the opening of said throttle valve and the engine speed, thus the extent of the spark produced by the plugs is constantly kept the same without change.
When the engine operates at idle or low speed, the mixture of air and fuel is denser, and the temperature of the plug is accordingly lowered by the fuel to such extent that carbon particles are apt to build up around the insulation of the intermediate electrode of the plug, possibly causing the failure of ignition and extinguishment of the combustion, incomplete combustion and fuel over-consumption.
Otherwise, a "warmer" plug can burn the accumulation of carbon particles away and further prevent the formation of those carbon particles. But an excessively hot plug can produce white or gray bulbous material on the insulation, causing faster wearing out of the plug as well as damage to the electrode. To overcome these problems, a method of controlling the extent of the spark and the pace of the ignition timing in accordance with the density of the mixed air and fuel is disclosed by the present inventor.